TensorFlow的reshape操作 tf.reshape的实现

初学tensorflow，如果写的不对的，请更正，谢谢！

tf.reshape(tensor, shape, name=None)

函数的作用是将tensor变换为参数shape的形式。

其中shape为一个列表形式，特殊的一点是列表中可以存在-1。-1代表的含义是不用我们自己指定这一维的大小，函数会自动计算，但列表中只能存在一个-1。（当然如果存在多个-1，就是一个存在多解的方程了）

好了我想说的重点还有一个就是根据shape如何变换矩阵。其实简单的想就是，

reshape（t, shape） => reshape(t, [-1]) => reshape(t, shape)

首先将矩阵t变为一维矩阵，然后再对矩阵的形式更改就可以了。

官方的例子：

# tensor 't' is [1, 2, 3, 4, 5, 6, 7, 8, 9]
# tensor 't' has shape [9]
reshape(t, [3, 3]) ==> [[1, 2, 3],
            [4, 5, 6],
            [7, 8, 9]]

# tensor 't' is [[[1, 1], [2, 2]],
#        [[3, 3], [4, 4]]]
# tensor 't' has shape [2, 2, 2]
reshape(t, [2, 4]) ==> [[1, 1, 2, 2],
            [3, 3, 4, 4]]

# tensor 't' is [[[1, 1, 1],
#         [2, 2, 2]],
#        [[3, 3, 3],
#         [4, 4, 4]],
#        [[5, 5, 5],
#         [6, 6, 6]]]
# tensor 't' has shape [3, 2, 3]
# pass '[-1]' to flatten 't'
reshape(t, [-1]) ==> [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6]

# -1 can also be used to infer the shape

# -1 is inferred to be 9:
reshape(t, [2, -1]) ==> [[1, 1, 1, 2, 2, 2, 3, 3, 3],
             [4, 4, 4, 5, 5, 5, 6, 6, 6]]
# -1 is inferred to be 2:
reshape(t, [-1, 9]) ==> [[1, 1, 1, 2, 2, 2, 3, 3, 3],
             [4, 4, 4, 5, 5, 5, 6, 6, 6]]
# -1 is inferred to be 3:
reshape(t, [ 2, -1, 3]) ==> [[[1, 1, 1],
               [2, 2, 2],
               [3, 3, 3]],
               [[4, 4, 4],
               [5, 5, 5],
               [6, 6, 6]]]

# tensor 't' is [7]
# shape `[]` reshapes to a scalar
reshape(t, []) ==> 7

在举几个例子或许就清楚了，有一个数组z，它的shape属性是(4, 4)

z = np.array([[1, 2, 3, 4],
     [5, 6, 7, 8],
     [9, 10, 11, 12],
     [13, 14, 15, 16]])
z.shape
(4, 4)

z.reshape(-1)

z.reshape(-1)
array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16])

z.reshape(-1, 1)
也就是说，先前我们不知道z的shape属性是多少，但是想让z变成只有一列，行数不知道多少，通过`z.reshape(-1,1)`，Numpy自动计算出有12行，新的数组shape属性为(16, 1)，与原来的(4, 4)配套。

z.reshape(-1,1)
 array([[ 1],
    [ 2],
    [ 3],
    [ 4],
    [ 5],
    [ 6],
    [ 7],
    [ 8],
    [ 9],
    [10],
    [11],
    [12],
    [13],
    [14],
    [15],
    [16]])

z.reshape(-1, 2)

newshape等于-1，列数等于2，行数未知，reshape后的shape等于(8, 2)

 z.reshape(-1, 2)
 array([[ 1, 2],
    [ 3, 4],
    [ 5, 6],
    [ 7, 8],
    [ 9, 10],
    [11, 12],
    [13, 14],
    [15, 16]])

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